Selecting management practices and cover crops for reducing tillage, enhancing soil quality, and managing weeds in western WA

Final Report for SW11-072

Project Type: Research and Education
Funds awarded in 2011: $196,626.00
Projected End Date: 12/31/2014
Region: Western
State: Washington
Principal Investigator:
Expand All

Project Information

Abstract:

In response to organic grower desires to improve soil quality through tillage reduction, while maintaining adequate weed control, we formed a research and producer group to plan research and extension activities matched to the unique climate, soil properties, and topography of western Washington. A summary of activities and findings under each of three project goals includes:

1) Identify production methods that effectively integrate cover crops and reduced tillage technologies to improve soil quality while reducing in-season weed pressure and seed bank populations on western WA organic farms.

Between 2012 and 2014 we initiated a multi-year reduced tillage cropping systems experiment and collaborated with organic producers to execute six on-farm experiments, one on-farm demonstration, and two cover crop selection trials.

The reduced tillage technologies evaluated to prepare soil for planting or transplanting included zone tillage (12-inch wide swath with a ground-driven strip tiller) and a no-till planting aid (disturbs a 2-inch swath of soil). Relative to complete tillage we found that soil at 5-10 cm in reduced tillage treatments was more compact and moist, and temperatures at 10 cm were 1.7 to 2.8 C cooler. Broccoli yields in research plots did not differ by tillage treatment in any of the three years, indicating no effect of reduction in tillage on broccoli yield. Squash yields were higher in full-tilled plots in 2012 and 2014. On-farm trials also indicated reduced squash yields with zone tillage relative to conventional tillage, especially in heavier-textured soils. However, broccoli planted to zone-tilled vetch performed as well as the farmer’s standard practice in two successive years with less equipment passes, but more time spent hand weeding.

In the fall of 2011 and 2012, cover crops were planted to evaluate variety, termination type, and termination time. Cover crops (five grains, five vetches, and seven mixes) were terminated at two different maturity stages: 60% and 100% flowering for vetches and late anthesis and early milk for grains. Cover crops were terminated with either flail mowing or a roller/crimper. The roller/crimper method was ineffective for vetches irrespective of termination date. Termination time influenced the effectiveness of rolling in grains; “early” was less effective than “late.” Termination time also influenced the percent weed cover (in 2013 only): “early” had fewer weeds than “late.” Rolled grains had lower weed percentage cover than did flailed grains. Termination by rolling was more effective for rye than barley. Vetches contained between 117 and 179 kg ha -1 N.

2) Evaluate profitability and greenhouse gas impacts of reduced tillage cropping systems on these farms.

Insitu soil respiration was consistently higher in the full-tillage treatment than in the reduced tillage treatment for the first seven days after tillage. The effect was most dramatic five hours after tillage when the spader treatment generated CO2 at a rate 1.5 to 2.2 times the rate in untilled areas. In both 2013 and 2014, tillage was significant on days 1, 3, and 7, with CO2 emissions higher in fully tilled plots than in the no-till plots. Emissions were highest on Day 0. CO2 emissions in both zones (In-Row and Out of Row) were similar within the full till treatment. The In-row zone occasionally produced higher emissions but was not consistently different, in the no-till treatment.

From an economic perspective, there was no significant difference among treatments in broccoli. Yield and time spent weeding were not significantly different in any of the three years studied. Both tractor-labor and fuel usage were greater in the spader treatment than in the reduced tillage treatments. Treatments utilizing the roller/crimper utilized about 0.5 hours less labor per acre than treatments utilizing the flail mower. Treatments utilizing the planting aid used about two gallons per acre less fuel than treatments using the strip tiller. For squash, there seems to be more yield potential in the spader treatment, as long as weeds are adequately controlled. Hand weeding times, the largest labor requirement in squash, were greater in the spader treatment in July 2012 and July 2013, but tractor cultivation done in June 2014 reduced the effort required for controlling weeds by hand in that year in the spader treatment.

3) Facilitate adoption of reduced tillage technologies and ideas to a wide audience.

Interest in incorporating cover crops and reducing tillage to improve soil quality is high among organic growers in Washington. Over the three year project we have directly reached 210 producers and professionals in six field-based events. Evaluations at each field day have helped us determine the degree to which our research has influenced growers' adoption of reduced tillage techniques and what remaining challenges exist. Agricultural professionals also attended the field days to increase their knowledge on the subject and better serve their clientele.

Weed management is an impediment to further adoption at cooperating farms in this study and presumably other diversified vegetable farms. We have learned that despite cover crop biomass as high as 7 Mg ha-1 and small percentages of weeds prior to termination, weeds will find their way through the mulch created by the terminated cover crop. When this happens, managing them is difficult. Also from our evaluations we hear consistently about barriers to adoption of reduced tillage organic practices. The barriers most often cited are: lack of access to specialized equipment, lack of a successful example that can be emulated, and worry about increased weed and pest pressure. Yet, the interest in reduced tillage organic agriculture continues to be high and we see potential for further adoption as new strategies are developed and equipment becomes more available.

Project Objectives:

Objective 1: Identify production methods that effectively integrate cover crops and reduced tillage technologies to improve soil quality while reducing in-season weed pressure and seed bank populations on western WA organic farms.

Performance targets:

  1. Through rigorous evaluation we will identify reduced organic no-till systems that are the most practical, economical, and beneficial to soil quality for Pacific NW vegetable producers.
  2. Weeds are a challenge when tillage and cultivation - the most common weed management tools for organic farmers – are removed or reduced. An important performance target will be to find cover crop species, cover crop management techniques, and cover crop termination strategies that combine to suppress weeds to the same degree as cultivation and tillage.
  3. Find cover crop varieties that mature early enough to be terminated and still plant or transplant a variety of cash crops. They must also produce sufficient biomass to cover the soil with a weed-suppressive mulch.
  4. Introduce leguminous cover crops into organic no-till rotation either alone or in combination with a grain cover crop to provide a nitrogen source while still serving a weed-suppressive function.

Objective 2: Evaluate profitability and greenhouse gas impacts of reduced tillage cropping systems on these farms.

Performance targets:

  1. Farm businesses that adapt new techniques must remain profitable to remain viable. To provide farmers with a broad analysis of reduced tillage cropping systems, we will compare relative profitability of these systems to their conventional counterparts. This will allow us to more fully address the viability of systems and also be extremely important in outreach.
  2. Provide regionally relevant information to growers for reduced till organic vegetable production.
  3. Consumers are increasingly aware of the environmental impacts of agriculture. Another performance target for our project will be to increase our understanding of greenhouse gas impacts from potential increased carbon storage and reduced fuel use and convey this information to growers and the public.

Objective 3: Facilitate adoption of reduced tillage technologies and ideas to a wide audience and identify tools and strategies most effective at encouraging behavior change.

Performance targets:

  1. Since our 2009 symposium and planning meeting, we have seen increased interest in reduced tillage in organic vegetable production. One of our “light house” farmers and cooperators, who already uses cover crops extensively, experimented this year with strip tillage (imposed with a walk-behind tiller) to grow winter squash surrounded by a mat of cover crop. Enabling, enhancing, learning from, and broadcasting this kind of experimentation and behavior change is an important performance target for our project.
  2. We will survey farmers throughout our field days and workshops to monitor their interest in adopting and willingness to try new soil conservation strategies such as reduced tillage. We will also survey and interview farmers to see what challenges they perceive to changing behavior around soil tillage. Identifying the top three or four strategies likely to result in behavior change will be another performance target.
  3. Facilitating farmers to overcome the obstacles to adopting reduced tillage will be another performance target. Equipment is likely to be one of these challenges, and working with local agencies such as conservation districts and NRCS personnel to help acquire appropriate technologies for use by interested farmers will be another performance target.

Research objectives 1 and 2 will be addressed by project researchers and producers by evaluating reduced-till cropping systems and cover crop varieties in the maritime NW through experiment station and on-farm trials. Outreach objective 3 will be addressed through evaluations and surveys of producers that participate in research and outreach events.

Introduction:

Many western Washington organic vegetable growers want to reduce tillage intensity, though few have tried due to challenges related to soil, weed management, and access to equipment (Corbin et al. 2013). Organic farmers typically employ combinations of soil inversion (with a moldboard plough), chisel ploughing, disking, spading, rototilling, and finishing tools to terminate cover crops, incorporate crop residue, control weeds, and prepare the seed bed for planting. Post-plant cultivation for weed management is also standard practice to uproot or bury emerged weeds.

Conservation or reduced tillage systems avoid soil inversion and reduce the depth of tillage from a typical 25-30 cm to 5-20 cm and also leave at least 30% of the soil surface covered with crop residue after seeding (Lal 1994; Carr et al. 2013). Zero- or no-till practices are an extreme form of reduced tillage that limit soil disturbance to only what is necessary to place a seed, such as disk openers preceded by narrow cutting coulters (Carr et al. 2013). Opening the soil to transplant vegetable seedlings in organic no-till systems has been accomplished by hand-digging (Leavitt et al. 2011), custom-made-tractor-drawn tools (Canali et al. 2013), or commercial no-till transplanters (Morse 2000).

Loss of precocity is a challenge to reduced-tillage vegetable production (Morse 1999). This is perceived as a real impediment for producers at higher latitudes where growing seasons are naturally shorter. Participants in a series of focus groups on tillage practices in western Washington (latitude 45º 30’ to 49º N) considered tillage to be a key method for increasing soil temperatures in the spring (Corbin et al. 2013). In a reduced-tillage experiment with zucchini in central Italy (latitude 42º 53’ N) soil temperatures at 0.1 m were consistently lower under a mulch created by rolling-crimping barley compared to a no cover crop control (Canali et al. 2013).

Zero- or no-till organic systems that use cover crop biomass as a surface mulch to suppress weeds have been explored more thoroughly in North America than in Europe (Carr et al. 2012). No-till vegetable production researchers have considered a cover crop mulch sufficiently thick to suppress weeds as desirable, though timely hand-weeding is often necessary to keep weeds below a yield-limiting threshold (Morse 2000; Díaz-Pérez et al. 2006). Seeding rate, timing of fall planting, spring termination date, and soil fertility can all affect cover crop biomass production (Mirsky et al. 2012). Climate and soil type interact directly and indirectly with these factors, necessitating the need for local and regional studies of biomass production and weed management capabilities of different cover crop varieties.

Several mechanical methods have been employed to terminate cover crops in organic production systems, including rolling and crimping, undercutting, flail mowing, and sickle bar mowing. In addition to the now common roller-crimper drum, (Morse 1999) describes other types of equipment that have been used to roll mature annual cover crops. A pioneering no-till organic farmer in Washington State used a front-mounted bucket and disengaged rototiller to flatten cover crops before acquiring a drum roller-crimper (Wayman & Collins 2013). The phenological stage of the cover crop affects the efficacy of rolling-crimping. Rolling before 50% anthesis (Zadoks 65) did not consistently control rye in a Maryland-based study that systematically examined termination times (Mirsky et al. 2009). Others have found that rolling at mid- to late-anthesis did not provide acceptable control of the cover crop, while rolling at soft dough (Zadoks 85) did (Ashford et al. 2000). Successful control of vetch with a roller crimper has been reported at the early pod stage (Mischler et al. 2010). Other researchers have had to continually mow vetch regrowth after rolling a mixed rye and vetch stand (Leavitt et al. 2011).

Some Pacific Northwest organic farmers are incorporating reduced tillage practices in their direct-market vegetable production, and they cite soil quality as a primary driver for their change in management practices (Wayman & Collins 2013). Tillage decreases soil organic matter (OM), aggregation, respiration, earthworms, and fungal-based food webs (Beare 1997; Franzluebbers 2002; Franzluebbers 1999). While conventional no-till systems have been used for years to improve soil, Teasdale et al. (2007) found organic practices, especially manure addition, increased OM to a greater degree. However, the authors examined only conventional no-till systems and did not examine the combined effects of organic practices and no-till.

Tillage reduces soil compaction, at least in the short-term. Overstreet & Hoyt (2008) found reduced bulk density in strip tilled zones compared to the untilled inter-row. Despite an increase in deep burrowing anecic earthworms, Peigné et al. (2009) found soils under reduced tillage had greater bulk density at 15-30 cm depth relative to moldboard ploughing. Different tillage strategies can also cause vertical stratification of soil quality parameters. Soils were more homogeneous from 0-30 cm in a moldboard plough treatment than they were in shallow tillage (soil disturbed with a rotary cultivator to 5-7 cm) after one year of treatment (Vian et al. 2009). Soil microbial biomass was reduced in the soil profile in the shallow tillage system due to greater compaction below 5 cm.

When compared to organically-managed systems using conventional tillage methods, reduced-tillage systems tend to produce equal or less vegetable yield. In Oregon, strip-tilled broccoli with cultivation produced 85.3% of the yield of the conventionally tilled control (Luna et al. 2012).

References Cited

Ashford, D.L. et al., 2000. Roller vs. herbicides: an alternative kill method for cover crops. In P.K. Bollich (ed.) Proceedings of the 23rd Annual Southern Conservation Tillage Conference for Sustainable Agriculture. Monroe, LA, pp. 64–69.

Beare, M.H., 1997. Fungal and bacterial pathways of organic matter decomposition and nitrogen mineralization in arable soils. In Brussaard, L. and R. Ferrera-Cerrato (Eds.). Soil Ecology in Sustainable Agricultural Systems. New York, NY: CRC Press, pp. 37–70.

Canali, S. et al., 2013. Conservation tillage strategy based on the roller crimper technology for weed control in Mediterranean vegetable organic cropping systems. European Journal of Agronomy, 50, pp.11–18.

Carr, P., Gramig, G. & Liebig, M., 2013. Impacts of Organic Zero Tillage Systems on Crops, Weeds, and Soil Quality. Sustainability, 5(7), pp.3172–3201.

Carr, P.M. et al., 2012. Editorial: Overview and comparison of conservation tillage practices and organic farming in Europe and North America. Renewable Agriculture and Food Systems, 27(01), pp.2–6.

Corbin, A.T. et al., 2013. Adoption Potential and Perceptions of Reduced Tillage among Organic Farmers in the Maritime Pacific Northwest. eXtension Foundation, eOrganic Community of Practice. Available at: http://www.extension.org/pages/68283/adoption-potential-and-perceptions-of-reduced-tillage-among-organic-farmers-in-the-maritime-pacific-n#.UthuUJKA35h.

Díaz-Pérez, J.C. et al., 2006. Effect of winter cover crops and no-till on the yield of organically-grown bell pepper (Capsicum annuum L.). In XXVII International Horticultural Congress-IHC2006: International Symposium on Sustainability through Integrated and Organic 767. pp. 243–248. Available at: http://www.actahort.org/books/767/767_25.htm [Accessed April 3, 2014].

Franzluebbers, A.J., 1999. Soil carbon, nitrogen, and aggregation in response to type and frequency of tillage. Soil Science Society of America Journal, 63, pp.349–355.

Franzluebbers, A.J., 2002. Soil organic matter stratification ratio as an indicator of soil quality. Soil and Tillage Research, 66, pp.95–106.

Lal, R., 1994. Tillage in the Corn Belt of the United States. In Carter, M.R., Ed. Conservation Tillage in Temperate Agroecosystems. Boca Raton, FL, USA: CRC Press: Lewis Publishers, pp. 73–114.

Leavitt, M.J. et al., 2011. Rolled winter rye and hairy vetch cover crops lower weed density but reduce vegetable yields in no-tillage organic production. HortScience, 46(3), pp.387–395.

Luna, J.M., Mitchell, J. & Shresta, A., 2012. Conservation tillage for organic agriculture: Evolution toward hybrid systems in the western USA. Renewable Agriculture and Food Systems, 27(1), pp.21–30.

Mirsky, S. et al., 2009. Control of Cereal Rye with a Roller/Crimper as Influenced by Cover Crop Phenology. Agronomy Journal, 101(6), pp.1589–1596.

Mirsky, S.B. et al., 2012. Conservation tillage issues: Cover crop-based organic rotational no-till grain production in the mid-Atlantic region, USA. Renewable Agriculture and Food Systems, 27(01), pp.31–40.

Mischler, R. et al., 2010. Hairy Vetch Management for No-Till Organic Corn Production. Agronomy Journal, 102(1), pp.355–362.

Mischler, R. et al., 2009. Hairy Vetch Management for No-Till Organic Corn Production. Agronomy Journal, 102(1).

Morse, R., 2000. High-residue, no-till systems for production of organic broccoli. In P.K. Bollich (ed.) Proceedings of the 23rd Annual Southern Conservation Tillage Conference for Sustainable Agriculture. Monroe, LA, pp. 48–51.

Morse, R.D., 1999. No-till vegetable production—its time is now. HortTechnology, 9(3), pp.373–379.

Overstreet, L.F. & Hoyt, G.D., 2008. Effects of Strip Tillage and Production Inputs on Soil Biology across a Spatial Gradient. Soil Science Society of America Journal, 72(5), p.1454.

Peigné, J. et al., 2009. Earthworm populations under different tillage systems in organic farming. Soil and Tillage Research, 104(2), pp.207–214.

Teasdale, J.R., Coffman, C.B. & Mangum, R.W., 2007. Potential Long-Term Benefits of No-Tillage and Organic Cropping Systems for Grain Production and Soil Improvement. Agronomy Journal, 99(5), p.1297.

Vian, J.F. et al., 2009. Effects of four tillage systems on soil structure and soil microbial biomass in organic farming. Soil Use and Management, 25(1), pp.1–10.

Wayman, S. & Collins, D.P., 2013. For the life of the soil: Farmer perspectives and experiences adopting reduced tillage organic agriculture. Tilth Producers Quarterly, 23(4), pp.1,4–5.

Cooperators

Click linked name(s) to expand
  • Colin Barricklow
  • Andy Bary
  • Chris Benedict
  • Craig Cogger
  • Andrew Corbin
  • Erick Haakenson
  • Steve Hallstrom
  • Sandra Wayman
  • Bethany Wolters

Research

Materials and methods:

Reduced-Tillage Cropping Systems: A multi-year reduced-tillage cropping systems experiment was initiated at the WSU Puyallup Research and Extension Center. The experiment includes five treatments that vary the type of cover crop termination and ground preparation: 1) roller/crimper+ no-till planting aid, 2) roller/crimper+ strip till, 3) flail mower + planting aid, 4) flail mower + strip till, and 5) flail mower + spader.

The experiment is a completely randomized block design with four replications (blocks). Blocks were arranged efficiently based on soil carbon and weed seed bank mapping using ad hoc power analysis. All plots were amended with compost and planted to ‘Strider’ barley September 2011. Three cash crops were planted to each treatment: squash, broccoli, and green beans and were rotated throughout the experiment.

Cover crop management and soil preparation: Cover crop were seeded in fall with a John Deere 10 ft. grain drill (model FBB, John Deere, Moline, IL). In 2011, all plots were seeded to ‘Strider’ barley at a rate of 113 lbs. per acre. In 2012 and 2013, ‘Purple Bounty’ vetch was planted in plots where broccoli would be grown and ‘Aroostook’ rye was planted in plots where squash and green beans were to be grown. Seeding rates for ‘Aroostook’ were 106 and 90 lbs./acre in 2012 and 2013, respectively. Seeding rates for ‘Purple Bounty’ were 84 and 139 lbs./acre in 2012 and 2013, respectively.

Cover crops in the Flail+Spader treatment were flailed (International Harvester IH-8094 flail mower (Rock Island, IL) in 2012 and a John Deere 370 (Moline, IL) in 2013-14) and then spaded (Imants spader, Reusel – NL, Italy). The Flail+PlantAid and Flail+StripTill treatments were flail mowed similarly to the tilled plots. A 2 m (6.5 foot) wide roller/crimper (I&J model 6FTCRO, Gap, PA) was used to terminate cover crops in the Roll+PlantAid and Roll+StripTill treatments. Vetch was planted before broccoli in all treatments and instead of rolling/crimping to terminate, these plots were flail mowed. Following rolling/crimping or flailing, the strip-till treatment was imposed with a Yetter strip tiller (Strip Builder, Colchester, IL) and the no-till planting aid treatment was imposed with a custom-built no-till planting aid consisting of a coulter and shank in-line (Figure 1).

‘Table Ace’ acorn squash was hand transplanted with 2 ft. in-row spacing and one row per 5 ft. bed with a Hatfield Transplanter (Johnny’s Selected Seeds, Model 2.0, 9414, Fairfield, MD). ‘Everest’ broccoli was transplanted with an Automatic Transplanter (Ellis Manufacturing Company, Inc, Model 450, Verona, WI) with 1 ft. in-row spacing and two rows per 5 ft. bed with 26 inches between row spacing. ‘Savanah’ beans were planted with a walk-behind Cole Planet Junior (Powell Manufacturing Company, Inc, Model B91-92B, Bennettsville, SC) with a target spacing of 2 inches in row and two rows per 5 ft. bed with 26 inches between row spacing. Crops were fertilized by hand annually, before planting with a 12-0-0 feather meal-based fertilize. We assumed 75% nitrogen availability from the fertilizer product and adjusted actual product application rates accordingly. Squash was fertilized at an expected N availability of 80, 120, and 120 lbs. available N / acre in 2012, 2013, and 2014, respectively. Broccoli rates were 160, 100, and 100 lbs. available N / acre in 2012, 2013, and 2014, respectively. Bean rates were 60, 80, and 80 lbs. available N / acre in 2012, 2013, and 2014, respectively. We reduced broccoli rates in 2013 and 2014 because of the addition of the vetch cover crop.

Cover crop biomass and maturity: Cover crop maturity was monitored by recording development stage with the Zadok’s scale (Zadok et al. 1974) for grains and by recording percent bloom for vetches (Mischler et al. 2010). Cover crop biomass and carbon and nitrogen content were calculated for each cover crop during spring of each year. Biomass was determined by harvesting the total aboveground biomass from two 0.25 m2 squares per plot. A subsample of this composited harvest was analyzed for carbon and nitrogen content using a combustion analyzer equipped with an infrared detector (LECO Instruments Model CNS 2000, LECO Instruments, St. Joseph, MI).

Soil quality parameters: Soil samples were focused on plots where squash was being grown and were taken from distinct areas around the plant zone to account for the varying widths of disturbance (i.e. the no-till planting aid creates a 5 cm disturbed zone, the strip tiller creates a 30 cm disturbed zone, and the tiller and spader disturb the entire plot). Bulk density, penetrometer, and infiltration were collected from an area centered 9 cm from the center of the row once per summer. Soil temperature and soil moisture were collected from the same zone at 30 minute and 60 minute intervals, respectively. In the strip till treatment, this area was subjected to strip tillage, but in the no-till treatment this area was undisturbed. Microbial biomass and soil nematodes were sampled from a 5 cm area in the center of the row, within the area of disturbance from the no-till planting aid once per summer. Soil nematodes were also sampled from an area centered 45 cm from the center of the row that was not disturbed by either strip tillage or the no-till planting aid. Nematodes were sampled only from the Flail+Spader and Roll+PlantAid treatments. Soil nitrate was sampled from a 30 cm zone in the center of the row, within the area disturbed by the strip tiller. Earthworms were also sampled from this area each year.

Bulk density was determined once mid-summer by intact cores collected with a hammer-driven core sampler (Grossman & Reinsch 2002). Soil nitrate was analyzed once post-harvest by a Cd reduction method (Gavlak et al. 2005). Infiltration was analyzed once mid-summer with the single-ring falling-head method (Soil Quality Institute 1999). Soil compaction was measured with a Rimik recording penetrometer (ICT International, Armidale, NSW, Australia) on August 18, 2011. Penetrometer readings were taken to a depth of 40 cm at nine locations per plot.

Nematodes were isolated from a 50-mL subsample by Baerman funnel modified with a wet-sieving step (Ingham 1994). Samples were collected after 48 hours on the funnel and stored at 4° C until they were enumerated at 25X magnification. A minimum of 100 individual nematodes were randomly selected from each sample and were then identified to genus or family level with the aid of an English translation of Bongers (1994) at 400 or 1000X, and community indices were computed (Bongers & Ferris 1999; Forge et al. 2003).

Earthworms were enumerated using a ‘hot’ mustard (allyl isothiocyanate) extraction technique (Lawrence & Bowers 2002). Two quadrats per plot (45.7 X 30.5 cm; 0.139 m2) were centered in the plant row. An additional two quadrats were taken 45 cm off center. Earthworms were divided between anecic (deep burrowing and larger) and endogeic (transient in the soil and smaller) earthworms.

Microbial biomass was determined with substrate-induced-respiration. The equivalent of 10 g oven dry, pre-incubated soil (adjusted to 40 to 50% water holding capacity and incubated at 25°C for 16 hpurs.) was dispersed to evenly cover the bottom of a half-pint canning jar (244 mL volume). Glucose solution was added with a syringe fitted with a 1.3-cm 27-gauge needle to bring the soil water content to between 75 and 80% water holding capacity and the glucose concentration to 20 μmol glucose g−1 soil solution. Following glucose addition, each jar was closed with an air-tight lid fixed with an intake and outtake in a 25°C incubator. Respiration rate was determined with a dynamic-closed-cell system (Heinemeyer et al. 1989). Each intake was connected to a manifold via a tri-valve that could be used to switch flow through the jar from an open system to a closed system. For the initial two hours the system was open; humidified, ambient air from outside of the building was passed continuously into all of the jars and then expelled from the outtake. Two hours after glucose addition, the tri-valve was switched to create a closed system; air from the outtake was passed through an infrared gas analyzer (LI-COR LI-7000) and then fed back through the jar. Carbon dioxide concentration was logged every second for 120 seconds and instantaneous respiration rate was then calculated by discarding the first 30 seconds and determining the rate of increase.

In-situ soil respiration was measured with a dynamic closed cell system and a portable infrared gas analyzer (Li-COR LI-7000). Chambers were 29.2cm x 49.5 cm with an average volume of 22.6 L and were designed similarly to the GRACEnet protocol with an extra port was to allow gas to be recirculate (http://www.ars.usda.gov/research/Gracenet). Readings were taken by attaching the lid and using the internal IRGA pump to circulate air between the chamber and the gas analyzer for 120 seconds with one reading per second. Instantaneous respiration rate was then calculated by discarding the first 30 seconds and determining the rate of increase. Soil respiration was measured in two treatments from the larger study: flail + spader and roll + planting aid. Measurements were also taken in the in-row area (centered over the middle of the plot) and in the out-of-row area (centered 45 cm away from the center of the plot).

Environmental Monitoring: Soil temperature was monitored hourly at 10 cm with temperature probes and a data logger (TMC20-HD Air/Water/Soil Temperature Probe & U12-008 4-Channel Outdoor External data logger; Onset Computer Corporation, Borne, MA). Light intensity (lumens ft-2) with light and temperature sensors (HOBO Pendant UA-002-08; Onset Computer Corp, Cape Cod, MA) were placed at the soil surface and below cover crop residue throughout the growing season at 15 minute intervals. Pendants were mounted with a rubber band on a small block of wood (7.6X 3.8 X 1.7 cm) to ensure the photo sensor was level. Mulch where the sensor was to be installed was carefully removed and set aside. Using a hand trowel a hole was dug deep enough to bury the sensor so the soil would evenly reach the upper most plane of the pendant but leave the sensor exposed. The mulch was then replaced overtop of the sensor to its original thickness, density, and structure. Soil moisture was monitored with Decagon Devices Em5b data loggers and 10HS Moisture Sensors.

Weed pressure: Weed densities in plots where squash was being grown were evaluated with quadrats (1/4m2) placed over row centers. Additionally, two biomass samples (1/4 m2) were taken prior to squash harvest, weighed, then dried and re-weighed. To reduce weed pressure, timed hand-weeding events occurred in all plots. Weeds were removed via hand pulling or with hand tools and total time spend weeding per plot and number of people hand-weeding was recorded. Tractor cultivation was employed in the Flail+Spader plots in 2014. Each spring, prior to cash crop planting, four soils cores (125in3) were taken from each squash plot. Samples were initially dried, then mixed with 500 g of soilless mix and placed into trays in a greenhouse (65F, 14:10 d:n). Emerged weeds were counted to the species level and stirred weekly. Once emergence stopped for three weeks, soil was bagged and placed into a freezer for one month. Samples were then placed back into the greenhouse and emerged weeds counted until germination ceased.

Crop yield and maturity. Squash and broccoli were harvested annually. Bean harvests were only made in 2014 because of poor overall establishment in 2012 and destruction by geese in 2013.                     

Statistical Analysis. Both the statistical packages R and SAS were used for statistical analyses using the procedures aov and lmer in R and glm SAS (R Development Core Team 2011; SAS Institute 2002). Assumptions of homogeneity and normality of variances were tested with visual observation (e.g. residuals versus fitted values) and with the Fligner-Killeen test for heteroscedasticity.

Cover Crop Trials: Winter cover crop varieties for the long-term systems experiment were selected in part based on trials conducted in 2011-2012 and 2012-2013 at WSU Puyallup. Cover crops were planted in fall and then their phenological development, biomass, and ability to be terminated with a flail mower and roller/crimper at two different dates (‘early’ and ‘late’) was monitored during the following spring and summer.

In 2011-2012, eight winter cover crops and two mixes were evaluated, including: ‘Alba’ barley, ‘Aroostook’ rye, common rye, common vetch, hairy vetch, ‘Lana’ vetch, ‘Purple Bounty’ vetch, ‘Strider’; mixes included: ‘Strider’ barley combined with either ‘Lana’ vetch or ‘Purple Bounty’ vetch. In 2012-2013, ten winter cover crops and six mixes were evaluated, including: ‘Strider’ barley, ‘Aroostook’ rye, common rye, ‘Merced’ rye, ‘Purple Bounty’ vetch, ‘Lana’ vetch, common vetch, hairy vetch, ‘Cahaba’ vetch, ‘Langadok’ vetch; mixes included ‘Purple Bounty’ combined with either ‘Strider’ ‘Aroostook’ or ‘Merced’ and common vetch combined with either ‘Strider’ ‘Aroostook’ or ‘Merced’ (Table 1).

The “early” target stage was Zadoks 67 (late anthesis) for grains and Mishler et al. 2010 stage 4 (60% flowering) for vetch, and the “late” target date was Zadoks 70 (early milk) and stage 5 (100% flowering). Termination time for the mix was determined based on the stage of either the grain or the vetch, whichever reached the target termination stage first. Termination effectiveness was assessed at four weeks by visually estimating percent cover crop erect after termination. In 2012, both grains and vetches were subjected to either rolling or flail mowing. Because of the lack of success in terminating vetches with rolling, in 2013 only grains were subjected to rolling; vetches were subjected to only flail mowing.

On-Farm Trials:

Over the three-year period, six replicated on-farm trials and one unreplicated on-farm demonstration were performed.

In 2012, on-farm trials were performed at Kirsop and Let Us Farm, and an on-farm demonstration was planted at Jubilee Farm. Kirsop compared two cover crops (‘Strider’ vs. ‘Strider’+crimson clover) and two tillage types (rototilling vs. strip tilling) with a randomized, strip block design with six replications for tillage type and two strips of ‘Strider’ +crimson clover and one strip of ‘Strider’ alone. At Let Us farm, all plots were planted to a mixture of ‘Strider’ +peas+red clover. Four replications were used to evaluate three termination type + tillage treatments: flail mower+spader, roller/crimper+strip tiller, and flail mower+ strip tiller. At Jubilee barley, pea and vetch were planted as summer cover crops, and chard and kale were fall transplanted with one replication.

In 2013, two on-farm trials were performed at Kirsop Farm and one was performed at Let Us Farm. In the first Kirsop trial, broccoli and kale were transplanted into flailed vetch with two ground preparation treatments: flail + strip tiller and flail + rototiller. There were two replications for each crop/treatment combination. In the other Kirsop trial, squash was transplanted to terminated ‘Aroostook’ rye. The cover crop termination and ground preparation treatments included: flail + strip tiller, roll+strip tiller, and flail+rototiller. There were four replications in a randomized block design. The Let Us Farm trial was identical to the Kirsop squash trial.

In 2014, one on-farm trial was performed at Kirsop Farm. Broccoli was transplanted into flailed vetch with two ground preparation treatments: flail + strip tiller and flail + rototiller. There were four replications in a randomized block design.

References Cited

Bongers, T., 1994. De Nematoden van Nederland, KNNV-bibliotheekuitgave 46. Pirola, Schoorl.

Bongers, T. & Ferris, H., 1999. Nematode community structure as a bioindicator in environmental monitoring. Trends in Ecology and Evolution, 14, pp.224–228.

Forge, T. et al., 2003. Effects of organic mulches on soil microfauna in the root zone of apple: implications for nutrient ?uxes and functional diversity of the soil food web. Applied Soil Ecology, 22, pp.39–54.

Gavlak, R., Horneck, D.A. & Miller, R.O., 2005. Soil Nitrate Nitrogen: KCl Extraction / Cd-Reduction Method. In Soil, Plant and Water Reference Methods for the Western Region. Western Regional Extension Publication, p. 199.

Grossman, R.B. & Reinsch, T.G., 2002. Bulk density and linear extensibility. In G.S. Campbell, R. Horton, and W.A Jury (eds.). Methods of Soil Analysis. Part IV: Physical Methods. Madison, WI: Soil Science Society of America, pp. 207–210.

Heinemeyer, O. et al., 1989. Soil microbial biomass and respiration measurements: An automated technique based on infra-red gas analysis. Plant and Soil, 116, pp.191–195.

Ingham, R.E., 1994. Ingham, R.E. 1994. Nematodes. p. 491–516. In R.W. Weaver et al. (ed.) Methods of soil analysis. Part 2. SSSA, Madison, WI. In R.W. Weaver et al. (ed.) Methods of soil analysis. Part 2. Madison, WI: SSSA, pp. 491–516.

Lawrence, A.. & Bowers, M.A., 2002. A test of the “hot” mustard extraction method of sampling earthworms. Soil Biology and Biochemistry, 34, pp.549–552.

Mischler, R. et al., 2010. Hairy Vetch Management for No-Till Organic Corn Production. Agronomy Journal, 102(1), pp.355–362.

R Development Core Team, 2011. R: A language and environment for statistical computing version 2.13.1.

SAS Institute, 2002. SAS STAT user’s guide, Cary, NC: SAS Institute.

Soil Quality Institute, 1999. Soil Quality Test Kit Guide. United States Department of Agriculture, Agricultural Research Service, Natural Resources, Conservation Service., pp.55–56.

Zadok, J.C., Chang, T.T. & Konzak, F.C., 1974. A decimal code for growth stages of cereals. Weed Research, 14, pp.415–421.

Research results and discussion:

Soil quality parameters

Soils in reduced tillage treatments were more compacted (Figure 2) and had greater bulk density (Figure 3) than soils in the spader treatment. Soil infiltration was slower in only the roll+planting aid treatments in 2012 relative to the other treatments. (Figure 4). Tillage effectively loosens soil and at least temporarily reduces compaction. In our experiment this did not also confer a change to the ability for water to infiltrate into the soil.

Surprisingly, there was not a distinct difference in the strip tilled treatments and the plant aid treatments. Bulk density, penetrometer, and spader were all taken in the strip-tilled zone, but out of the plant aid zone. We expected the strip tilled soil to exhibit different physical properties than the less disturbed plant aid zone. However, the strip tiller is ground driven and not motorized via a power take-off (PTO), which limits its ability to disturb the soil. Also, it is cutting through a large amount of plant residue, which tends to bind in the tiller and likely reduces its effectiveness.

There was no difference in microbial biomass among management systems in either 2012 or 2014. Data were not taken in 2013. Nematodes were sampled and isolated, but community analysis is still underway. Earthworms were sampled each year during the spring, which is the most active time of worm activity. The soil in this area ranges from 55 to 66% sand. Earthworms are less abundant in sandy soils and populations were too low to get meaningful data with the isothiocyanate incubation. We were able to isolate numerous earthworms on the same day from a different, less sandy (~30% sand) part of the farm with similar methodology.

In previous research we have seen that that long-term undisturbed soils, such as in a pasture or grass alley, have high microbial biomass relative to cultivated treatments. On the other hand, recently-tilled soils (e.g. one to three weeks) can also have a slightly elevated microbial biomass. Since none of our treatments involved long-term reduced tillage, it is not unusual that there was no difference in microbial biomass.

Insitu soil respiration was consistently higher in the full-tillage treatment than in the reduced tillage treatment for the first seven days. The effect was most dramatic five hours after tillage when the spader treatment generated CO2 at a rate 1.5 to 2.2 times the rate in untilled areas (Figure 6). In both 2013 and 2013, tillage was significant on days 1, 3, and 7, with CO2 emission higher in fully tilled plots than in the no-till plots (Figure 7). Emissions were highest on Day 0. CO2 emissions in both zones (In-Row and Out of Row) were similar within the full till treatment. The In-row zone occasionally produced higher emissions but was not consistently different in the no-till treatment.

Environmental Monitoring:

All reduced-tillage treatments obscured more light than the fully tilled treatment (Figure 8). Rolling/crimping obscured slightly less light than flail mowing (Figure 8a) and the plant aid treatment obscured more light than the strip till treatment (Figure 8b). Light pendants were in place within the strip tilled zone, so we expected a more dramatic difference in light penetration between strip tilling and plant aid.

Similarly to the light penetration, all reduced-tillage treatments had lower soil temperature than the spader treatment (Figure 9). Rolling/crimping had lower soil temperature than flail mowing (Figure 9a). There was little separation between the plant aid treatment and the strip till treatment (Figure 9b). As with light penetration, temperature probes were in place within the strip tilled zone, so we expected a more dramatic difference in light penetration between strip tilling and plant aid.

Soils were dryer throughout most of the growing season in the spader treatment relative to the reduced tillage treatments (Figure 10). Rolling/crimping maintained higher soil moisture than flail mowing during the month of August (Figure 10a). There was little difference between the plant aid treatment and the strip till treatment (Figure 10b). Increased soil moisture during the driest months is a potential benefit of the reduced tillage treatments. On the other hand, the tilled soil dried out more quickly in the late spring and early summer, which may have contributed to higher soil temperatures (Figure 9).

Weed pressure: As described above, weeds were counted within a month of transplanting and just prior to harvest (2012 & 2014). In 2013 and 2014 weed density was significantly greater in fully tilled plots within one-month after transplanting (Figure 11). This difference, however was not present prior to harvest. This could be attributed to the weed management activities that were deployed throughout the course of the growing season. Weed seed bank data is still being captured through the greenhouse grow-out. Preliminary analysis shows a trend towards numeric reduction in active weed seed bank densities in reduced tillage plots.

Weed biomass was assessed just prior to harvest (2102 & 2014 only) and showed no statistical difference between treatments (Figure 12). This can be attributed to the within-season weed suppressive activities.

To capture a sense of weed management needs, timed hand weeding events occurred on an as needed basis and was tallied throughout the trial. In 2012, early season handweeding was significantly lower in reduced tillage squash plots in squash (Figure 13). This trend did not follow in 2013 where no differences were observed in reduced tillage plots (the flail+spader treatment was an exception) and in 2014 fully tilled plots required significantly lower hand weeding times. Across season temperature and moisture condition differences combined with historic weed seed inputs could explain this variation. Until weed seedbank assessments are finalized we cannot conclude this trends is in fact the case. Hand weeding times were not different in broccoli during any of the hand weeding events (Figure 14).

Crop yield and maturity.

Cover crop termination and reduced tillage combinations did not affect broccoli yields during any of the three years of the trial (Figure 15). Full tillage (flail spader) bore greater squash yields than reduced tillage treatments in both 2012 and 2014 (Figure 16). Flail mowing produced greater squash yields in 2012 and 2014, among reduced tillage treatments (Figure 17).

Strip tilling yielded more squash in 2012, but plant aid yielded more in 2014 (data not shown).

Cover Crop Trials.

Biomass production by different cover crops in the two cover crop trials are listed in Table 2. Among the grains, ‘Aroostook’ rye was a consistently high biomass producer.

The percentage of cover crop that was weeds and the weed biomass is presented in Table 3. ‘Aroostook’ and hairy vetch both performed well in terms of suppressing weed biomass. In combinations, common vetch combined with grains tended to perform better than ‘Purple Bounty’ vetch combined with grains.

The N concentration, C:N ratios, and N in kg ha-1 are given in Table 4. Hairy and common vetch produced the most N kg ha-1, though there was no significant difference among vetches. Though there was not a synergistic effect in terms of biomass production by mixes (Table 2), mixes did have the advantage of contributing N to the soil system.

Grain species and varieties matured differently in the spring, and this affects the timing for terminating with reduced-tillage options (Figure 18). ‘Strider’ barley matured more quickly than either rye variety. The ryes tended also to spend more time in the anthesis stage, which is a critical stage for termination. Barley heads, on the other hand, tends to emerge already in pollination and move from anthesis to milk quickly. ‘Aroostook’ matured more quickly than common rye and reached the end of anthesis about two weeks sooner than common rye.

The time difference between “early” and “late” termination was between 10 to 18 days, depending on cover crop variety and maturation rate. Termination time influenced the effectiveness of roller-crimping; rolling at the “early” stage (late anthesis) had less effective kill than at the “late” stage (early milk) (Table 5). Grain cover crops were more likely to return upright after having been rolled at the earlier stage. Termination time also influenced percent weed cover (in 2013 only); “early” termination had fewer weeds than did “late” termination (Table 6). If mowing cover crops, terminate early for lower percent weed cover. Earlier termination also allows a longer growing season for cash crops. But if rolling grain cover crops, wait to terminate until the “later” stage (early milk) to attain mulch that stays flat.

Termination time did not influence cover crop biomass, winter weeds, cover crop N concentration, or C:N ratio. Waiting to terminate will not increase the amount of biomass or N that cover crops produce.  

We found that rolled grains had less weed cover than did flailed grains. However, there are other considerations besides weed management when choosing a termination method: cover crops may not always kill completely when roller-crimped and may stand upright again. When flailed, cover crops are chopped into pieces and full-kill will occur; however flailed crops may be more likely to decompose sooner than rolled. We found that rolling was effective for rye but not for barley. Vetches and grain-vetch mixes were not included in the roll-flail comparison because vetches could not be effectively killed by rolling.

On-Farm Trials.

Replicated on-farm trials were performed at Kirsop Farm and Let Us Farm. Squash yields were consistently lower at Let Us Farm with strip tillage than they were with the farmer’s common practice of rototilling. The soils at Let Us Farm are a silt loam and are much heavier than the loamy sand at Kirsop farm. At Kirsop, squash yields were much lower in 2012 with strip tillage. In 2013, there was large variability within the experiment and no detectable difference in yield. Broccoli and kale following strip tilled common vetch performed as well as rototilling at Kirsop farm in both 2013 and 2014 (Table 7).

References Cited

Wayman, S.S., 2013. The influence of cover crop variety, termination timing, and termination method on mulch, weed cover, and soil nitrate in organic reduced-tillage. In in Wayman, S.S. Cover crops and weed dynamics in organic reduced tillage. M.S. Thesis. Pullman, WA: Washington State University, pp. 93–120.

Research conclusions:

Interest in incorporating cover crops and reducing tillage to improve soil quality is high among organic growers in Washington. Over the three year project we have directly reached 210 producers and professionals in six field-based events. Evaluations at each field day have helped us determine the degree to which our research has influenced growers' adoption of reduced tillage techniques and what remaining challenges exist. Agricultural professionals also attended the field days to increase their knowledge on the subject and better serve their clientele.

In a retrospective, post-field day evaluation in 2012, most participants (61%, n=18) considered themselves to have moderate or advanced experience with cover crops. However, only 33% considered themselves to have moderate or advanced experience with reduced tillage. Four out of six of the attendees that had incorporated reduced-tillage in their farming practices indicated that they had been influenced to do so through observations and knowledge gained at previous WSU No-Till Extension events, especially observation of field trials. Lack of specialized equipment was frequently listed as the largest impediment to more adoption. Fifty-six percent of the field day attendees were farmers and 60% of the farmers were certified organic. 

A second 2012 field day at WSU Puyallup focused on monitoring greenhouse gases in agriculture. The audience was mostly agriculture professionals (53%) and graduate students (33%). In a retrospective, post-event evaluation (n=15) most attendees reported that they had a moderate (40%) or advanced (47%) understanding of organic agriculture, while only 13% self-identified as beginners to organic agriculture. When asked about their understanding of greenhouse gases in agriculture respondents were less confident, with 27% describing their knowledge as beginner, 47% moderate, and only 27% advanced.  

At a field day in 2013 at WSU Puyallup, a retrospective, post-field day evaluation (n=24), 54% of participants considered themselves to be at a beginning level with cover cropping and 75% considered themselves to have little to no experience with reduced tillage organic agriculture. Four producers indicated they had adopted some reduced tillage practices while another 16 producers indicated that they felt equipment, knowledge, and weed control were still challenges to their ability to adopt these techniques. A total of 39 people attended the event and a farmer collaborator assisted in presenting to producers at the field day.

At a field day in 2014, a participatory evaluation/focus group was conducted to evaluate the impacts of the project and hear how attendees are adopting reduced tillage and what barriers they saw. Attendees were most interested in reduced tillage as a means to reduce inputs, protect soil heath (e.g. conserve organic matter, increase biodiversity, soil fertility), and manage weeds. Many attendees had incorporated reduced tillage, though primarily on a smaller scale. Examples of methods used by attendees included mulching with burlap bags or straw. One producer had fashioned their own roller crimper. Another uses field rotation and summer cover cropping, allowing tillage to be reduced during the year when cash crops are not grown. Barriers to incorporating more reduced tillage included invertebrate pests (e.g. wireworm, slugs), rhizomatous weeds, timing, equipment, and cost. Several attendees intended to employ reduced-tillage techniques they had seen demonstrated, including using a modified BCS walk-behind rototiller for strip tillage. Twenty-seven farmers, gardeners, and agricultural professionals attended the field day.

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

Presentations and Articles.  

In 2012, results of our work were presented at the 6th National Small Farms Conference, Memphis TN, and two separate presentations were delivered at the Tilth Producers of Washington Regional Conference.

In 2013, results of our work were presented at the Agronomy Society of America, Tampa FL, the Tilth Producers of Washington Regional Conference, Yakima, WA, and the Weed Science Society of America Annual Meeting. An article in the Tilth Producers Quarterly focused on producers that are adopting reduced tillage organic agriculture. Another peer-reviewed article published in eOrganic described focus group research on adopting reduced tillage organic agriculture.

In 2014, a peer-reviewed publication was accepted by Renewable Agriculture and Food Systems and another is under review in Weed Technology. Poster presentations were made at the Agronomy Society of America meeting in Long Beach, CA and at the Tilth Producers of Washington Annual Conference in Vancouver, WA.

Presentations

Collins, D.P, C. Benedict, A. Bary, C.G. Cogger, Sandra Wayman, A. Corbin. 2014. Selecting management practices and cover crops for reducing tillage, enhancing soil quality, and managing weeds in western WA organic vegetable farms. WSU BIOAg Symposium, Pullman, WA. Poster Presentation.

Wolters, B.R., Collins, D.P., Fortuna, A.M., Cogger, C.G., Bary, A. 2014. Greenhouse gas emissions in no-till vegetable production. Proceedings of the Agronomy Society of America. Long Beach, CA. Poster Presentation

Fortuna, A.M, D.P. Collins, C. Cogger. 2014. Management to reduce N2O emissions in Organic Vegetable Production Systems. eOrganic Webinar.

Benedict, C., S. Wayman, D. Collins, C. Cogger, A. Bary, A. Corbin. 2014. Evaluation of an Organic Reduced Tillage System in the Pacific Northwest and the Influence on Weed Populations. Weed Science Society of America/Canadian Weed Science Society. Vancouver, British Columbia. Poster Presentation.

Collins, D.P, A.M. Fortuna, B. Wolters, A. Bhowmik, C.G. Cogger, A. Bary, R.F. Turco. 2013. Greenhouse gas emissions and soil quality in long-term integrated and transitional reduced tillage organic systems. BioEarth Conference. Pullman, WA. Poster Presentation.

Bary, A., Wayman, S. D.P. Collins, C. Cogger, C. Benedict. 2013. Tillage reduction and cover cropping for enhanced soil quality and weed management in western Washington organic vegetable farms. Northwest Horticultural Society Annual Meeting. Oral Presentation.

Wayman, S., C. Cogger, C. Benedict, I. Burke, and D. Collins. 2013. Choosing and managing cover crops to improve weed management in reduced tillage organic vegetable production. Proceedings of the Soil Science Society of America, Tampa, FL. Poster Presentation.

Collins, D., C. Cogger, A. Bary, C. Benedict, D. Corbin, and C. Miles. 2012. Tillage reduction and cover cropping for enhanced soil quality and weed management in western Washington organic vegetable farms. Proceeding of the 6th National Small Farms Conference. Memphis, TN.

Collins, D., C. Cogger, A. Bary, C. Benedict, D. Corbin, C. Miles, C. Barricklow, and S. Hallstrom. 2012. Tillage reduction and cover cropping for enhanced soil quality and weed management in western Washington organic vegetable farms. Tilth Producers of Washington Annual Conference. Port Townsend, WA. Invited Speaker.

Benedict, C. and I. Burke. 2013. Cultural Methods of Organic Weed Management. Tilth Producers of Washington Annual Conference. Port Townsend, WA. Invited Speaker.

Articles

Wayman, S., C. Cogger, C. Benedict, I. Burke, D. Collins, and A. Bary. Submitted. Cover crop effects on light, nitrogen, and weeds inorganic reduced tillage. Weed Technology.

Wayman, S., C. Cogger, D. Collins, C. Benedict, I. Burke, and A. Bary. 2014. The influence of cover crop variety, termination timing, and termination method on mulch, weed cover, and soil nitrate in organic reduced-tillage. Renewable Agriculture and Food Systems. FirstView: 1-11. http://dx.doi.org/10.1017/S1742170514000246.

Wayman, S. and D. Collins. 2013. For the life of the soil: Farmer perspectives and experiences adopting reduced tillage organic agriculture. Tilth Producers Quarterly. 23 (4): 1, 4-5.

Corbin, A., D. Collins, R. Krebill-Prather, C. Benedict, and D. Moore. 2013. Adoption potential and perceptions of reduced tillage among organic farmers in the maritime Pacific Northwest. eXtension Foundation, eOrganic Community of Practice. [Online]. http://www.extension.org/pages/68283/adoption-potential-and-perceptions-of-reduced-tillage-among-organic-farmers-in-the-maritime-pacific-n#.UthuUJKA35h

Email listserve

Organic Reduced Tillage in the Pacific Northwest, http://eorganic.info/node/8246

Grower Field Days:

In 2012, four grower field days reached a total of 144 participants; in 2013, one field day attracted 39 participants; and in 2014 one field day attracted 27 participants.

Project Outcomes

Project outcomes:

From an economic perspective, there was no significant difference among treatments in broccoli. Yield (Figure 15) and time spent weeding (Figure 14) were monitored on a plot level so data could be evaluated statistically. Treatments were not significantly different in any of the three years studied. Harvesting, irrigating, fertilizing, and planting also utilize hand labor, but these activities were consistent across treatments (Figure 19). Both tractor-labor and fuel usage were greater in the spader treatment than in the reduced tillage treatments (Figure 21). Treatments utilizing the roller/crimper utilized about 0.5 hours less labor/acre than treatments utilizing the flail mower. Treatments utilizing the planting aid used about two gallons/acre less fuel than treatments using the strip tiller (Figure 21).

Squash yields were larger in the fully tilled spader treatment than in the reduced tillage treatments in 2012 and 2014, but lower in 2013. For squash, there seems to be more yield potential in the spader treatment. In 2013, hand weed control was not adequate, and the spader treatment performed worse than the other treatments. In 2012 and 2014, weed management was better and the spader treatment yielded the most. Hand weeding times were greater in the spader treatment in July 2012 and July 2013 (Figure 13, Figure 20). In June 2014, we machine cultivated the spader treatment, and this likely reduced the effort required for managing weeds in the June 2014 weeding (Figure 14). As with broccoli, treatments utilizing the roller/crimper utilized about 0.5 hours less labor/acre than treatments utilizing the flail mower. Treatments utilizing the planting aid used about two gallons/acre less fuel than treatments using the strip tiller (Figure 22).

Farmer Adoption

There are few farms in the maritime northwest that utilize the type of reduced tillage organic agriculture practices that we have trialed in this experiment. Two farms that have extensively adopted some of these techniques were profiled in an article for Tilth Producers Quarterly by Sandra Wayman (formerly a graduate student on this project) and Doug Collins (project director) (Wayman & Collins 2013).

The first farm profiled was Cascadian Home Farm, Rockport, WA. In brief:

  • They practice rotational reduced tillage. After one year of no-till pumpkins, the land is rotated to a different crop where conventional tillage methods are used.
  • Cover crops are intended to provide weed suppressing mulch.
  • Pumpkins are not irrigated, possibly reducing weed pressure during the growing season.

The second farm profiled was Good Earth Center, San Juan Island, WA. In brief:

  • Work is done with hand tools.
  • Cover crops are scythed several times during the spring, then terminated by scraping at the soil line with a shallow hoeing. Residue is raked off the plots before seeding; more is left in place for transplants.
  • Transplanting, direct seeding, and succession sowing are all integrated into the reduced tillage system.
  • Crops are watered with drip irrigation.
  • Soils are never tilled, even for seeding cover crops. The deepest disturbance happens while transplanting.

Two of our farmer-cooperators in this project, Steve Hallstrom (Let Us Farm) and Colin Barricklow (Kirsop Farm), are interested not only in reduced tillage but also in novel ways to use and manage cover crops. Steve Hallstrom engages in a type of reduced tillage by doing whole field rotation. Cash crops are only planted in a particular piece of ground every other year and summer and winter cover crops are used to nourish the resting ground. Attempts to transfer the management strategies developed at WSU Puyallup (roller/crimper or flail mower for termination and strip tiller for ground preparation) have been much less successful at Let Us Farm then at Kirsop farm. The heavier soil at Let Us has presented problems with root penetration and plant establishment.

Prior to participating in on-farm experiments in this project, Colin Barricklow had experimented with reduced tillage in the form of a living mulch of clover in squash production. They had utilized a rototiller to till a strip and then planted squash in the strip and mowed the clover until the squash made mowing impossible. Through on-farm experiments we have developed a model with Colin Barricklow of successfully planting broccoli into flail-mowed vetch, with the ground prepared with a Yetter Strip Builder. Yields have been equal to rototilled controls, but hand-weeding has been more time consuming. The tilled soil provides a clean surface that can be easily cultivated with a tractor. This greatly reduces the time required for hand-weeding.

Weed management is an impediment to further adoption at both Let Us Farm and Kirsop Farm, and presumably other diversified vegetable farms. We have learned at both sites, and at WSU Puyallup, that despite cover crop biomass as high as 7 Mg ha-1 and small percentages of weeds prior to termination (e.g. 5-10%), weeds will find their way through the mulch created by the terminated cover crop. When this happens, controlling them is difficult.

At Let Us Farm, there also seemed to be a problem with plant establishment in the heavy soil. Many farmers working with heavier soils find that they need to cross the fields several times to prepare a good planting bed – ploughing, disking, tilling, disking again, finishing, etc. Our single pass with a ground-driven strip tiller at Let Us Farm did not prepare the soil to the same degree that it did at Kirsop Farm.

We have also queried farmers at our field days about their experiences with reduced tillage. Through these exercises we have found that some farmers are utilizing some aspects of reduced tillage, including: terminating cover crops with flail mowers or home-made crimpers, using broad forks to open the soil for planting, and mulching with burlap sacks or straw. These techniques have been primarily adopted on very small-scale farms or large gardens.

Also from our evaluations we hear consistently about barriers to adoption of reduced tillage organic practices. The barriers most often cited are: lack of access to specialized equipment, lack of a successful example that can be emulated, and worry about increased weed and pest pressure. Yet, the interest in reduced tillage organic agriculture continues to be high and we see potential for further adoption as new strategies are developed and equipment becomes more available.

Recommendations:

Areas needing additional study

Through this collaborative research project we have made significant progress in describing suitable cover crops and management strategies for reduced tillage in organic agriculture. Furthermore, we have established that in the sandy loam soil at WSU Puyallup and the loamy sand at Kirsop Farm, broccoli can be grown with reduced tillage techniques as effectively as with full tillage.

Adopting techniques to reduce tillage in organic agriculture still presents risks to growers. The primary risks we have observed are in effectively managing weeds and in promoting plant establishment in heavier soils. Future research should focus on reducing risk for early adopters of reduced tillage by addressing these limiting factors. Continuing to share successes and failures will help experiment with systems that can be incorporated into their own operations. Specific future research directions could include:

  • Develop and analyze best strategies for cover crop residue management in zone tilled organic agriculture systems. Modify existing strip tillage to provide more aggressive in-row tillage.
  • Evaluate nitrogen cycling dynamics in reduced tillage organic systems: 
  • Continue to evaluate cover crops and termination strategies for reduced tillage organic agriculture: successful cover cropping is essential to reducing risk in adopting reduced tillage organic vegetable production. The cover crop must produce enough biomass to effectively suppress weeds and also reach a late developmental stage to mechanically terminate while accommodating a relatively short growing season.
  • Can cover crop termination be moved earlier in the spring? Loss of precocity is a challenge to reduced-tillage vegetable production (Morse 1999). This is perceived as a real impediment for producers at higher latitudes where growing seasons are naturally shorter.
  • Develop and analyze strategies for long-term continuous reduced tillage in organic agriculture: to date we have not experimented with continuous reduced tillage methods in northwest Washington.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.